1. Field of the Invention
The present invention relates to a power supply unit including a number of cells connected in series and being used for an electric vehicle such as a pure electric car, etc. In more detail, the present invention relates to a radiator of cells constituting the power supply unit.
2. Description of the Prior Art
In general, in an electric vehicle such as a pure electric car, etc., in order to supply a motor etc. with electric power for driving a vehicle, a power supply unit including a number of cells connected in series is mounted. In this way, a number of cells connected in series are used as a power supply unit of an electric vehicle, it is necessary to dispose a plurality of cells densely from the viewpoint of space efficiency, etc. Therefore, plural rows of storage batteries in which a plurality of cells arranged in a row and electrically connected in series are disposed in parallel.
When a plurality of cells are disposed densely as mentioned above, the temperature in the power supply unit is raised due to heat generation, Joule heat or the like of the cells, thus raising the temperature of each cell. Therefore, conventionally, a method for suppressing the temperature rise of each cell by allowing a coolant such as air, etc. to circulate between cells has been employed.
However, the conventional cooling method increases the difference in temperature between cells, which may lead to a variation of the battery performance, for example, charge-discharge capacity or life, etc., between cells. Therefore, the reliability as a power supply unit was low.
In order to reduce the difference in temperature between cells, JP10 (1998)-3950A proposes a power supply unit including a group of storage batteries in which plural rows of storage batteries including a plurality of cells connected in series in a row are disposed in parallel above and below and left and right of a coolant passage for allowing a coolant to circulate between the rows of the storage battery, wherein the coolant passage includes a main coolant passage that is exposed to the cells within the same storage battery row and a sub-coolant passage whose upstream side is separated from the storage battery row and whose downstream end is connected to the main coolant passage at the position corresponding to the midstream or downstream end of the storage battery row. With this configuration, the following effects can be obtained. Namely, the temperature of the coolant circulating in the main coolant passage is increased by the endothermic from the cells of the upstream of the storage battery rows and the cooling efficiency at the midstream and downstream is deteriorated. However, in the midstream and the downstream of the main coolant passage, by combining the coolant circulating in the main coolant passage with a low temperature coolant, the temperature of the coolant is lowered. Thus, the cooling efficiency of the cells at the further downstream can be enhanced to reduce the difference in temperatures within the storage battery row.
However, there is a problem in that with the configuration of the power supply unit suggested in JP10 (1998)-3950A, the structure of the case housing the storage battery row (battery module) becomes complicated. Namely, a battery holding member for holding the storage battery row (battery module) is necessary, and also an idea for forming a sub-coolant passage, or for connecting the main coolant passage with the sub-coolant passage at the position corresponding to the midstream or downstream of the storage battery row (battery module) is necessary. Furthermore, since the cross-sectional area of the passage is small, the pressure loss of the coolant is increased, thus deteriorating the cooling efficiency.
It is an object of the present invention to provide a power supply unit in which the structure of the battery case can be simplified and a cross sectional area of the passage is increased to improve the cooling efficiency.
In order to achieve the above-mentioned object, a power supply unit according to the present invention includes; a battery case, a plurality of battery modules disposed in parallel, each battery module being composed of three cells or less connected in series, and the front end and the rear end of the battery module being held by the front part and the rear part of the battery case, a cooling system for forcing a coolant to flow in a passage between the neighboring battery modules, and a shielding system placed at the upstream side of the coolant passage and shielding the coolant from the battery module. According to the configuration of this power supply unit, since each battery module is composed of three cells or less, when the front end and the rear end of the battery module are held by the front part and the rear part of the battery case, the cells positioned in the middle part are held securely by the cells positioned at both ends. Consequently, it is possible to prevent the connection parts of the battery module from being deviated or detached from each other due to the vibration from the outside. Therefore, since a battery holding member other than the holding means for the front part and the rear part of the battery case is not required, the structure of the battery case can be simplified. Furthermore, for the same reason, since a cross-sectional area of the passage between the neighboring battery modules can be increased, it is possible to reduce the pressure loss of the coolant and to improve the cooling efficiency. Furthermore, since the means for shielding the coolant from the battery module is provided at the upstream side of the coolant passage, the heat amount that the coolant entering the passage between the neighboring battery modules within the battery case can absorb from the cell placed at the upstream side is reduced. Therefore, since the temperature of the coolant is not increased due to the heat of the cell placed at the upstream side of the coolant passage, it is possible to cool the cell at the midstream and downstream efficiently. In particular, since the battery module is composed of three cells or less, as compared with the battery module composed of four cells or more, it is possible to reduce the variation in temperatures between cells. Therefore, the temperature difference between cells within the battery module can be reduced. Thus, it is possible to suppress the variation of the battery performance such as charge/discharge capacity or life, etc. As a result, the reliability as a power supply unit can be enhanced.
Furthermore, it is preferable that the configuration of the power supply unit of the present invention includes means for increasing the flow rate of the coolant, the means being placed at the downstream side of the coolant passage. With this preferable configuration, it is possible to improve the cooling efficiency of the cells positioned at the downstream side of the coolant passage. Furthermore, in this case, it is preferable that the means for increasing the flow rate of the coolant is a wedge-shaped rectifying fin protruding into the battery case.
Furthermore, in the power supply unit of the present invention, it is preferable that a detachable first constraint plate is further provided at the front part of the battery case and the front end of the battery module is held by the first constraint plate. According to this configuration, after the battery module is housed in the battery case, the battery modules can be held in the battery case. Furthermore, in this case, it is preferable that an air inlet port is provided in the first constrained plate, which is placed between the neighboring battery modules and draws the coolant into the battery case from the outside, and the means for shielding the coolant from the battery module is integrated into the first constraint plate with the air inlet port sandwiched therebetween. According to this preferable configuration, since the means for shielding the coolant from the battery module is integrated into the first constraint plate, the number of the components can be reduced.
Furthermore, it is preferable in the power supply unit of the present invention that the means for shielding the coolant from a battery module is provided approximately in parallel to the battery modules while protruding into the battery case.
Furthermore, it is preferable that the power supply unit of the present invention satisfies the relationship: L/2 less than mxe2x89xa6L, where L denotes a length of the cell, and m denotes a length of the shielding system for shielding the coolant from the battery module. According to this preferable configuration, heat exchange amount can be reduced.
Furthermore, in the power supply unit of the present invention, it is preferable that a second constraint plate is further provided at the rear part of the battery case and the rear end of the battery module is held by the second constraint plate. Furthermore, in this case, it is preferable that an exhaust port for exhausting the coolant to the outside from the inside of the battery case is provided in the second constraint plate, and a means for increasing the flow rate of the coolant is integrated into the second constraint plate. According to this preferable configuration, since the means for increasing the flow rate of the coolant is integrated into the second constraint plate, the number of the components can be reduced.